Mysterious HP-19C power-on behavior



#9

I have two HP-19C's that have the exact same strange behavior. I've had trouble with the batteries on both, or so I thought. I will get them working, then a few days later, they don't turn on. I didn't realize until today that I didn't need to "fiddle around" with the battery packs. After a few minutes of removing them, adjusting the cells, etc., they would finally turn on.

Today, I just spent time turning the power switch on and off. After a few minutes, and some intermittent powering up, they both power up reliably.

Any idea what component has begun to fail in both? I assume it's a capacitor. Has anyone else had observed this strange behavior?


#10

Have you cleaned the power switch contacts?


#11

Once they're on, the switches seem quite reliable. I can sure try. The keyboards are heat-staked, so it could be a challenge...


#12

Oh, so it uses the same keyboard design as the Woodstocks? I've never opened mine, so I didn't know, and just asumed that the contacts could be accessed w/o tearing the keyboard apart. I have found similar behavior on other calcs with dirty power switch contacts. It's like a milli-volt drop test - the current eventually overcomes the high contact resistance and closes the circuit.

#13

I haven't taken my 19C's apart in a while (I have 2 also). But I think you might be able to drip a bit of DeoxIT into the switch contact area from the back of the heat-staked keypad. I've done this a few times with woodstocks that have the same problem and it's worked well.

-Katie


#14

Hi Katie! That's exactly what I did tonight. Both calcs are turning on fine now, as expected. I'll let you know their behaviors in a couple of days. The stuff seeps through to the front, so I'll have to repolish them also to get the switches looking right again.


#15

Thanks Michael and Katie. Both calculators still show the exact same behavior... taking many attempts to finally turn on, then turning on flawlessly after that!!!!

Any other thoughts??


#16

Do you have a regulated DC power supply you can connect directly to the battery contacts? I've gotten weird behavior with some of my battery packs that did not seem to make consistent contact. Worth a try. Also, is continuous memory being retained? I assume you are getting no display in either program or run mode. Finally, try placing the printer in manual mode before you switch it on. As soon as you switch it on, even though you get no display, hit PRX, and see if there is any printer activity.


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